Electrolytic apparatus using a hydrogen storage cathode

ABSTRACT

An electrolytic apparatus which comprises effecting electrolysis of an electrolytic solution in an electrolytic chamber separated from a reaction chamber by a hydrogen-storing metal member with one surface of the hydrogen-storing metal member as a cathode opposing an anode so that hydrogen thus produced is adsorbed by the hydrogen-storing metal member while allowing hydrogen thus adsorbed and a material to be treated to undergo continuous catalytic reaction in the reaction chamber on the other surface of the hydrogen-storing metal member to cause hydrogenation or reduction reaction by hydrogen thus adsorbed, wherein an electrolytic apparatus having a porous catalyst layer provided on the catalytic reaction surface of the hydrogen-storing metal member is used.

This is a divisional of application Ser. No. 09/131,677 filed Aug. 10,1998, now U.S. Pat. No. 6,224,741 the disclosure of which isincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to an electrolytic process which comprisesa continuous reaction in which active hydrogen converted from hydrogenproduced by electrolysis takes part, e.g., a hydrogenation reaction anda hydrogen reduction reaction, an apparatus therefor and a process forthe production of an electrode for use in such an electrolyticapparatus.

BACKGROUND OF THE INVENTION

A hydrogen reaction in which active hydrogen takes part, e.g., ahydrogenation reaction of organic material is employed in variouschemical fields. In accordance with the cracking reaction of petroleum,for example, gasoline or kerosene can be obtained from heavy oil.Further, reaction which comprises liquefying tar content so that it isadapted more for the purpose is actually practiced. Moreover, theconversion of unsaturated hydrocarbon to saturated hydrocarbon ispracticed.

Some hydrogenation reactions are often allowed to proceed in a uniformsystem. For example, an organic material is hydrogenated in the presenceof a contact catalyst. It is known that a noble metal such as palladiumis an excellent catalyst for the hydrogenation reaction of anunsaturated organic compound (S. Siegel, in “Comprehensive OrganicSynthesis”, ed., B. M. Trost and I. Fleming, Pergamon Press, Oxford,1991, vol. 8). These reactions are disadvantageous in that they requirea high pressure reaction vessel or normally require a relatively hightemperature that can cause the explosion depending on the purity of thehydrogen gas used in hydrogenation. These reactions are alsodisadvantageous in that the catalyst used has an insufficient reactionselectivity and thus side reactions can occur.

In order to enhance reaction selectivity and reduce energy consumption,electrolytic reduction, which is a heterogenous system reaction, may beemployed as described in A. M. Couper, D. Pletcher and F. C. Walsh,“Chem. Rev.”, 1990, 90, 837, T. Nonaka, M. Takashashi and T. Fuchigami,“Bull. Chem. Soc. Jpn.”, 182 56, 2584, M. A. Casadei and D. Pletcher,“Electrochim. Acta, 33, 117 (1988), T. Yamada, T. Osa and T. Matsue,“Chem. Lette.”, 1989 (1987), L. Coche, B. Ehui, and J. C. Moutet, “J.Org. Chem.”, 55, 5905 (1990), and J. C. Moutet, Y. Ouennoghi, A. Ourariand S. Hamar-Thibault, “Electrochim. Acta”, 40, 1827 (1995). Anelectrode catalyst having a large surface area such as Raney nickel canbe used for an electrochemical hydrogenation reaction and thus can beexpected to provide a high power efficiency. Further, such an electrodecatalyst provides safe and easy operation. However, this system requiresthat the organic material to be treated be electrically conductive.Otherwise, an additive must be added to the organic material to renderthe organic material electrically conductive.

As described above, hydrogenation reactions can be divided into twotypes, i.e., homogeneous system reactions and heterogeneous systemreactions. It is known that atomic hydrogen produced on the catalystacts to accelerate the reaction in either case.

As one of other processes for safely effecting hydrogenation reaction ata high efficiency, a process is known which comprises bringing thereaction compound to be hydrogenated into contact with palladium orother hydrogen-storing metals (metal hydride) having hydrogen heldtherein. It is said that palladium or many hydrogen-storing alloys alsohave a catalytic action in this reaction and thus can fairly act in thereaction. However, this process is disadvantageous in that once hydrogenadsorbed in the hydrogen-storing metal alloy or palladium is consumedfor the reaction with a small amount of the reactant, the reaction nolonger proceeds even if the remaining reactant is left unreacted. Thus,this process can be performed batchwise only. This process can beperformed reasonably well on an experimental basis but at an extremelylow efficiency on an industrial basis.

In order to solve these problems, the inventors proposed the followingprocess and apparatus. In other words, electrolysis is effected in anelectrolytic solution with one surface of a plate-like hydrogen-storingmetal as a cathode to produce hydrogen. The hydrogen thus produced isthen adsorbed by the plate-like hydrogen-storing metal at one surfacethereof. The hydrogen is diffused into the hydrogen-storing metalthrough which it moves to-the other surface thereof. The reactant to behydrogenated is brought into contact with the other surface of thehydrogen-storing metal at which a hydrogenation reaction or a reductionreaction by hydrogen is continuously effected. It has been obvious thatthis process and apparatus can find wide application in the industry andcan produce a hydrogenated product at a high efficiency.

However, this reaction process is disadvantageous in that thehydrogenation reaction often is a rate-limiting step. The inventors madeextensive studies of this reaction process. As a result, the followingfacts were found. When the current density is raised to accelerate theproduction of hydrogen by electrolysis, the rate of production ofhydrogen exceeds the highest allowable value for hydrogenation reactionat an early stage. Even if hydrogen is present in excess, thehydrogen-storing metal can keep adsorbing and holding hydrogen.Therefore, hydrogen thus produced is rarely wasted. However, this islimited. If the current density is raised beyond a predetermined value,the current efficiency is reduced so much. In other words, this reactionprocess is disadvantageous in that the productivity of hydrogenatedproduct cannot be increased beyond a certain limit.

SUMMARY OF THE INVENTION

It is therefore one object of the present invention to provide anelectrolytic process and apparatus which can operate in the hydrogenreaction chamber at a hydrogen reaction rate corresponding to theincrease in the rate of production of hydrogen accompanying the increasein the electrolysis rate and maintain the current efficiency at a veryhigh value with respect to the electrolytic current for producinghydrogen.

Another object of the present invention is to provide a process for theproduction of an electrode for the above purpose.

The above-described objects of the present invention are accomplished bythe following embodiments of the present invention:

(1) An electrolytic process which comprises effecting electrolysis of anelectrolytic solution in an electrolytic chamber separated from areaction chamber by a hydrogen-storing metal member with one surface ofthe hydrogen-storing metal member as a cathode opposing an anode so thathydrogen thus produced is adsorbed by the hydrogen-storing metal memberwhile allowing hydrogen thus adsorbed and a material to be treated toundergo continuous catalytic reaction in the reaction chamber on theother surface of the hydrogen-storing metal member to cause ahydrogenation or reduction reaction by hydrogen thus adsorbed, whereinthat an electrolytic apparatus having a porous catalyst layer providedon the catalytic reaction surface of the hydrogen-storing metal memberis used.

(2) An electrolytic apparatus comprising an electrolytic chamber and areaction chamber separated by a hydrogen-storing metal member, anelectrolytic solution charged in the electrolytic chamber, and an anodeprovided opposing the hydrogen-storing metal member in the electrolyticchamber as a cathode, wherein that the hydrogen-storing metal membercomprises a porous catalyst layer taking part in a hydrogen reaction onat least a part of the surface thereof in contact with the reactivecompound in the reaction chamber.

(3) The electrolytic apparatus according to embodiment (2) above,wherein the hydrogen-storing metal is palladium or an alloy thereof, theporous catalyst layer is a metal black belonging to the platinum groupor gold and the hydrogen reaction in which the catalyst takes part is areduction reaction involving the hydrogenation of an unsaturatedhydrocarbon.

(4) The electrolytic apparatus according to embodiment (2) above,wherein the porous catalyst layer formed on the surface of thehydrogen-storing metal member is obtained by bringing a hydrogen-storingmetal member which has adsorbed hydrogen into contact with anelectroless plating solution containing a catalyst component so that thesurface of the hydrogen-storing metal member is electrolessly platedwith the catalyst metal by the action of hydrogen adsorbed in thehydrogen-storing member.

(5) A process for the production of an electrode which comprisessubjecting an electroless plating solution containing a cation of ametal which serves as a catalyst to electrolysis with one surface of ahydrogen-storing metal body being in contact with an electrolyticsolution while the other being in contact with the electroless platingsolution with the hydrogen-storing metal body serving as a cathode, thecathode being opposed to an anode in contact with the electrolyticsolution to produce on the cathode side hydrogen which is then adsorbedin the hydrogen-storing metal body through which hydrogen moves andreaches the other surface thereof on which it is desorbed therefrom toproduce active hydrogen by which the metallic cation in the electrolessplating solution is reduced so that the hydrogen-storing metal body isplated with the catalyst metal on the surface thereof in contact withthe electroless plating solution, whereby the catalyst component isattached to the hydrogen-storing metal body and the contact area forreaction is enlarged.

(6) The process for the production of an electrode according toembodiment (5) above, wherein the hydrogen-storing metal body is apalladium or palladium alloy plate, the metal cation in the electrolessplating solution is an ion of a metal belonging to the platinum group orgold and the component which serves as a catalyst to be attached to thehydrogen-storing metal body is a metal black belonging to the platinumgroup or gold.

(7) The process for the production of an electrode according toembodiment (5) or (6) above, wherein the electroless plating solutioncontains a cation of at least one metal selected from the groupconsisting of gold, silver, nickel, copper, lead and metallic elementsbelonging to the platinum group.

BRIEF DESCRIPTION OF THE DRAWINGS

By way of example and to make the description more clear, reference ismade to the accompanying drawings in which:

FIG. 1 is a schematic diagram illustrating a section of an electrolyticcell used in the electrolytic process of the present invention;

FIG. 2 is a schematic diagram illustrating an embodiment of theelectrolytic apparatus of the present invention used in the electrolyticprocess of the present invention:

FIG. 3 is a graph illustrating the cumulative amount of palladium blackdeposited during electrolysis;

FIG. 4 is a graph illustrating the relationship between the cumulativeproduced amount of 4-ethyltoluene and the reduction reaction time; and

FIG. 5 is a graph illustrating the relationship between the depositiontime of palladium and the reaction efficiency of 4-ethyltoluene, whereinin the above figures the reference numeral 1 indicates an electrolyticcell, the reference numeral 2 indicates a hydrogen-storing metal plate(cathode), the reference numeral 3 indicates an electrolytic chamber,the reference numeral 4 indicates a hydrogenation reaction chamber, thereference numeral 5 indicates an anode, the reference numeral 6indicates an anodic gas outlet, the reference numeral 7 indicates areactant solution feed opening, the reference numeral 8 indicates areflux opening, the reference numeral 9 indicates a power supply, thereference numeral 10 indicates a porous catalyst layer, the referencenumeral 11 indicates a circulating tank, and the reference numeral 12indicates a roller pump.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be described in more detail below.

In the present invention, a hydrogen reaction is a reaction in whichactive hydrogen takes part, such as a hydrogenation reaction. Specificexamples of hydrogenation reactions include a hydrogenation reaction anda hydrogen reduction reaction. Examples of these hydrogenation reactionsinclude reactions for converting methylstyrene to ethyl toluene,cracking reactions of petroleum, and reactions for producing gasoline orkerosene from heavy oil.

FIG. 1 is a schematic diagram illustrating a section of an electrolyticcell used in the electrolytic process of the present invention.

FIG. 2 is a schematic diagram illustrating an embodiment of theelectrolytic apparatus of the present invention used in the electrolyticprocess of the present invention.

The electrolytic cell 1 shown in FIGS. 1 and 2 is adapted for thehydrogenation reaction of the reactant. The electrolytic cell 1 iscoated with Teflon on the interior side thereof. As shown in FIG. 1, theelectrolytic cell 1 is partitioned into an electrolytic chamber 3 and ahydrogenation reaction chamber 4 by a thin plate-like or foil-likehydrogen-storing metal plate 2. The hydrogen-storing metal plate 2 has aporous catalyst layer 10 provided on the surface thereof facing thehydrogenation reaction chamber 4. An aqueous solution of potassiumhydroxide as an electrolytic solution is charged in the electrolyticchamber 3. The hydrogen-storing metal plate 2 is connected to a powersupply 9. The hydrogen-storing metal plate 2 forms a cathode on theelectrolytic chamber side thereof. Provided opposed to the cathode 2 andin the vicinity of the side wall is a plate-like anode 5. The anode 5 ismade of nickel. However, the anode 5 may be made of stainless steelrather than nickel. The reference numeral 6 indicates an anodic gasoutlet in which an electrolytic solution feed opening may be provided.

Provided in the reaction chamber 4 are a reactant solution feed opening7 and a reflux opening 8. As shown in FIG. 2, a circulating tank 11connected to the electrolytic cell 1 and a roller pump 12 are providedso that the reactant can be circulated. The electrolytic cell 1 and thecirculating tank 11 are communicated to each other via a connecting pipemade of fluororubber.

Into the hydrogenation reaction chamber 4 of the electrolytic cell 1 issupplied a solution of an organic compound such s styrene in an organicsolvent from the circulating tank 11 by the action of the roller pump12. At the same time, the electrolytic chamber 3 is filled with anelectrolytic solution such as an aqueous solution of potassium hydroxideas mentioned above. When ah electric current from the power supply 9 isapplied across the anode 5 and the hydrogen-storing metal plate as acathode, hydrogen is produced by electrolysis in the electrolyticchamber 3. The hydrogen thus produced is adsorbed by thehydrogen-storing metal plate (cathode) 2. The hydrogen thus adsorbed isthen transmitted by the hydrogen-storing metal plate 2 in the directionperpendicular to the surface thereof. The hydrogen then reaches thehydrogenation reaction chamber side thereof at which it then comes incontact with and hydrogenates the organic compound such as styrene toproduce ethylbenzene. During this process, the porous catalyst layer 10provided on the hydrogenation reaction chamber side of thehydrogen-storing metal plate 2 accelerates the hydrogenation reaction.

The solution containing the reactant thus hydrogenated is circulatedthrough the reflux opening 8 and the circulating tank 11. If necessary,the solution is again hydrogenated in the electrolytic cell 1.

The hydrogen-storing metal plate 2 needs to be electrically-conductiveand stable as a cathode during electrolysis. Preferably, thehydrogen-storing metal plate 2 has some catalytic activity forhydrogenation reaction. If possible, the hydrogen-storing metal plate 2must satisfy the requirements that it should show little volumetricchange during occlusion and release of hydrogen and should have littletendency toward embrittlement after repeated adsorption and release ofhydrogen. Representative examples of such a material include palladium,which belongs to the platinum group, and palladium alloy. Palladium isknown to exhibit an extremely high hydrogen permeability. Further,palladium has some catalytic activity. Thus, palladium is one of themost desirable metals. Palladium alloyed with a small amount of gold oraluminum is resistant to embrittlement and is suitable for manypurposes. Lanthanum-nickel alloy, alloy containing a rare earth elementsuch as mischmetal, titanium alloy, zirconium alloy, etc., too, areuseful as hydrogen-storing metal plate.

It is usual that the thickness of the hydrogen-storing metal plate issufficiently thin from the standpoint of efficiency of hydrogenationreaction. In order to subject the hydrogen-storing metal plate toelectrolysis as a cathode, the hydrogen-storing metal plate needs tohave some thickness. In general, the thickness of the hydrogen-storingmetal plate is preferably from 0.01 to 2 mm, but there is no reason whythis plate should be limited to this range. It may be properlydetermined according to the electrolytic conditions. Thehydrogen-storing metal plate adsorbs and transmits hydrogen and acts asa power supplying material. Therefore, if used as a part of industrialfacilities, the hydrogen-storing metal plate may be made of a metal foilclad with a metal mesh or the like.

In the present invention, the hydrogen-storing metal member used in thiselectrolytic apparatus comprises a porous catalyst layer 10 provided onthe catalytic reaction side thereof, which faces the reaction chamber,to accelerate the hydrogenation reaction.

In some detail, the hydrogen-storing metal member comprises a porouscatalyst layer 10 formed on at least a part of the surface thereof incontact with the reaction compound in the hydrogenation reaction chamber4. The term “catalyst” as used herein is meant to indicate a catalystwhich takes part in and accelerates, e.g., a hydrogenation reactioninvolving the hydrogenation and conversion of styrene to ethylbenzene.Because of its porosity, the catalyst layer allows the hydrogen-storingmetal plate to maintain its capability of adsorbing and desorbinghydrogen and hence desorption sites for adsorbed hydrogen on the surfacethereof.

The catalyst to be used in the catalyst layer of the hydrogen-storingmetal plate is a catalyst which takes part in the hydrogenationreaction. For example, metals belonging to the platinum group,particularly palladium, platinum, iridium and ruthenium can be used.Besides these metals, noble metals such as gold and silver can be used.Further, nickel, copper, lead, etc. can be used. Other catalystmaterials may be appropriately selected depending on the kind of thehydrogenation reaction to be effected in the presence thereof. A metalhaving a catalytic action alone may be selected. However, a catalystmetal is preferably selected which can be easily provided with a surfacearea large enough to increase the possibility of contact with thereactant. From this standpoint of view, a metal black belonging to theplatinum group or gold, particularly palladium black, which is free ofluster, is often most desirable. This is because palladium black has alarge surface area and thus can form a catalyst layer which exerts anextremely excellent effect of catalyzing the hydrogenation reaction oforganic materials. Further, palladium is also capable of adsorbing anddesorbing hydrogen besides these capabilities.

The provision of the foregoing catalyst on the hydrogen-storing metalplate in the form of porous layer can be accomplished, e.g., by thefollowing method. In some detail, an electroless plating solution havingcations of catalyst metal component dissolved therein is prepared. Ahydrogen-storing metal plate having hydrogen adsorbed therein is thenallowed to come in contact with the electroless plating solution so thatthe cations of catalyst metal component are reduced by hydrogen thusdesorbed in a required amount. In this manner, the catalyst componentthus reduced is attached to the hydrogen-storing metal plate as adeposit having a required sufficient thickness, leaving desorption sitesfor adsorbed hydrogen.

The catalyst layer thus formed has a structure such that active hydrogenwhich is desorbed from the hydrogen-storing metal plate to take part ina hydrogen reaction such as a hydrogenation reaction can be suppliedfrom the vicinity of the catalyst. In this arrangement, the catalystlayer can provide a desired product at a far greater efficiency thancatalyst layers prepared otherwise.

The electroless plating solution is not specifically limited. If thehydrogen-storing metal plate is plated with platinum or palladium as acatalyst, the electroless plating solution may be hydrochloric acid orsulfuric acid with a salt containing such an element incorporatedtherein. The salt concentration of the electroless plating solution ispreferably from 1 to 100 g/l, and the acid concentration of theelectroless plating solution is preferably from 1 to 100 g/l. Forexample, the electroless plating solution preferably contains HCl andPdCl₂ in an amount of 36.5 g/l and 5 g/l, respectively, to allow easyproduction of dull black deposit. The electroless plating solutionpreferably comprises a slight amount of lead ion dissolved therein to.produce palladium black.

In the foregoing formation of the catalyst layer, the electrolytic cell1 shown in FIG. 1 may be advantageously used because it allowscontinuous processing.

The hydrogenation reaction chamber 4 is filled with the electrolessplating solution while the electrolytic chamber 3 is filled with theelectrolytic solution. Under these circumstances, an electric current isapplied across the anode 5 and the hydrogen-storing metal plate(cathode) 2 so that hydrogen is produced at the hydrogen-storing metalplate (cathode) 2.

The electrolytic aqueous solution to be injected into the electrolyticchamber 3 preferably does not corrode the hydrogen-storing metal plate 2and the electrically-conductive plate 2, which acts as an electrode. Forexample, an aqueous solution of potassium hydroxide is desirable. Thehydrogen-storing metal plate 2 on which a catalyst is to be provided ispreferably sufficiently rough. This is because the plating reaction canproceed smoothly when the contact area of the hydrogen-storing metalplate with the plating solution is sufficiently large. Thehydrogen-storing metal plate 2 is preferably subjected to blastfinishing or etching on the surface thereof to be plated in thehydrogenation reaction chamber 4. The degree of such a surface treatmentis not specifically limited. The blast finishing may be accomplished bythe use of alumina grit having a size of from 15 to 20 meshes. The blastfinishing provides an increase of effective surface area twice or threetimes.

The density of electrolytic current applied during plating may be suchthat the production of hydrogen gas is not observed on the surface ofthe hydrogen-storing metal plate 2. In some detail, it is preferablyfrom 0.1 to 10 A/dm², particularly from 1 to 5 A/dm². If the currentdensity falls below 0.1 A/dm², the plating takes too much time. Inparticular, if a metal having no hydrogen permeability such as platinumis provided as a catalyst, the resulting deposit is so dense thatdesorption sites on the hydrogen-storing metal plate are blocked, easilyinhibiting the plating reaction by atomic hydrogen. On the contrary, ifthe current density exceeds 10 A/dm², it accelerates the deformation ofmetal. Further, the amount of hydrogen gas released from theelectrolytic cell increased. The plating metal is deposited more in theform of dendrite. The resulting deposit exhibits a reduced strength.

When a hydrogen-storing metal such as palladium and palladium alloy isallowed to come in contact with hydrogen, it adsorbs hydrogen on thesurface thereof from which hydrogen is then adsorbed by the interior ofthe metal.

When an aqueous electrolytic solution such as an alkali solution issubjected to electrolysis in the electrolytic chamber 3 with thehydrogen-storing metal plate 2 as a cathode provided opposing an anode,hydrogen is produced on the hydrogen-storing metal plate (cathode) 2. Inthis manner, atomic hydrogen is produced.

H₂O+e→H_(ad)+OH⁻  (1)

The atomic hydrogen thus produced is then adsorbed as active hydrogen bythe surface of the hydrogen-storing metal plate 2 on the electrolyticchamber side. The active hydrogen is then adsorbed deep in thehydrogen-storing metal plate 2 without being desorbed therefrom.

H_(ad)→H_(ab)  (2)

H_(ad) represents adsorbed hydrogen, and H_(ab) represents adsorbedhydrogen. The active hydrogen which has thus been adsorbed deep in thehydrogen-storing metal plate 2 then diffuses into the hydrogen-storingmetal plate 2. Thus, the active hydrogen is then rendered desorbable onthe inner side of the hydrogenation reaction chamber 4.

When the hydrogen-storing metal plate 2 which has adsorbed atomichydrogen is allowed to come in contact with the plating solutioncontaining cations, the cations are reduced by the atomic hydrogen. Thematerial which has thus been reduced and lost electric charge is thendeposited on the surface of the hydrogen-storing metal plate 2. At thesame time, the atomic hydrogen becomes hydrogen ion which is thendesorbed from the hydrogen-storing metal plate 2.

The foregoing reaction mechanism is represented by the following, usingpalladium for example as a plating metal:

Pd²⁺+2H_(ab)→Pd+2H⁺  (3)

If the plating metal is palladium, the deposit can be thickened becausepalladium can transmit atomic hydrogen. Even if an ion of a metalliccomponent having no capability of adsorbing hydrogen such as platinum,gold and copper is used to plate the hydrogen-storing metal, plating maybe effected on one surface of the hydrogen-storing metal plate whileatomic hydrogen migrates from the other surface thereof to the onesurface thereof. In this manner, the thickness of the deposit of theplating metal is nonuniform over the migration paths of hydrogen. Thehydrogen-storing metal is partially exposed on some migration paths. Asa result, a thick porous deposit having a very large effective surfacearea can be obtained. The electroless plating of the hydrogen-storingmetal can be effected in the hydrogenation reaction chamber 4 at thesame time with the hydrogen adsorption and permeation reaction byelectrolysis in the electrolytic chamber 3.

Platinum or gold exhibits characteristics close to that of palladium,although its mechanism is unknown.

The hydrogen-storing metal which has been plated with a specificcatalyst may be further plated with another catalyst metal. In order toform another metal layer on the metal plate, electrolytic plating methodis normally employed. In accordance with electrolytic plating method,the entire surface of the hydrogen-storing metal can be uniformlycovered. Thus, this method is basically not preferred in the presentinvention. However, if the hydrogen-storing metal has been plated withpalladium black to have a sufficient surface area, the upper layer maybe formed by electrolytic plating method or electroless plating method.

In order to form a deposit by an electrolytic plating method, anelectric current is applied to the electrode thus electrolessly platedwhile the electrode is being dipped in an electrolytic solution asdesired plating solution. Using platinum as an example, the chemicalmechanism is given below.

Pt⁴⁺+4e→Pt  (4)

The hydrogen production reaction by electrolysis can be appropriatelycontrolled by adjusting the current density within a wide range. Theamount of hydrogen which can be adsorbed in the hydrogen-storing metal,if it is palladium or the like, is extremely large, though this willdepend on the conditions. When electrolysis is effected at a currentdensity as high as 10 A/dm² or above with no previous adsorption ofhydrogen in the hydrogen-storing metal, hydrogen is produced, but littleor no production of gas is observed. Almost all the amount of hydrogenthus produced is immediately completely adsorbed by the hydrogen-storingmetal. As hydrogen is adsorbed in the hydrogen-storing metal on onesurface thereof, the hydrogenation reaction of, e.g., styrene, proceedson the reaction chamber side at a rate corresponding to the rate ofproduction of hydrogen. In general, however, a hydrogenation reaction ora hydrogen reduction reaction proceeds at a lower rate than anelectrochemical reaction. The inventors made extensive studies ofacceleration of hydrogenation reaction or reduction reaction to the rateof production of hydrogen. The present invention has thus been workedout.

The present invention will be further described in the followingexamples, but the present invention should not be construed as beinglimited thereto. Unless otherwise indicated, all parts, percents, ratiosand the like are by weight.

EXAMPLE 1

Using an electrolytic apparatus as shown in FIG. 2, a palladium plate asa hydrogen-storing metal was plated with palladium black on the surfacethereof.

A palladium plate having a thickness of 0.1 mm was inserted as a cathodeinto an electrolytic cell 1 at the center thereof. A platinum platehaving a thickness of 0.5 mm as an anode was provided opposing thecathode in an electrolytic chamber 3. The electrolytic chamber 3 wasfilled with a 6M aqueous solution of caustic potassium as anelectrolytic solution. The cathode plate had a cathode area of 1 cm².

A reaction chamber 4 was filled with an aqueous solution of palladiumchloride as a reaction solution (plating solution, hereinafter referredto as “reaction solution”). Under the following conditions, an electriccurrent was applied to the electrolytic chamber 3 with the reactionchamber 4 filled with the electroless plating solution of palladiumchloride so that the palladium plate was electrolessly plated withpalladium on the plating chamber side thereof.

Reaction solution: PdCl₂ 5 g/dm³+HCl 1 mol/dm³

Current density: 1 A/dm² (10 MA)

Agitation: None

Electrical quantity: 5C (coulomb)

Reaction formula: Pd²⁺+2H.→Pd+2H⁺

When the current efficiency was 30%, palladium black was deposited to athickness of 0.5 μm. When observed on an SEM photograph, a granulardeposit having a size of 1 μm was confirmed. The plating of thehydrogen-storing metal with the catalyst was then completed.

Thereafter, a reduction reaction was conducted in the same manner asmentioned above except that the reaction chamber 4 was filled with4-methylstyrene rather than the foregoing reaction solution. Theintroduction of the reactant was accomplished by the action of a rollerpump through a fluororubber tube. The reaction conditions in thereaction chamber 4 were as follows:

Reaction substrate: 4-Methylstyrene

Temperature: Room temperature

Flow rate: 2.5 ml/min

Loading: 6 ml

Current density: 5 A/dm² (50 mA)

Electrolysis time: 5 hours

Under the foregoing conditions, electrolysis was effected. When thecurrent efficiency was 30%, 4-ethyltoluene was obtained.

COMPARATIVE EXAMPLE 1

The reduction reaction was effected in the same manner as in Example 1except that palladium black was not deposited on the palladium plate.When the current efficiency was not more than about 0.1%, 4-ethyltoluenewas obtained.

EXAMPLE 2

Using the same electrolytic cell 1 as used in Example 1, palladium blackwas deposited on a palladium plate under the following conditions:

Reaction solution: PdCl₂ 5 g/dm³+HCl 1 mol/dm³

Current density: 1 A/dm² (10 mA)

Agitation: None

Electrical quantity: 36C

When the current efficiency was 30%, palladium black was deposited to athickness of 2.5 μm. The deposit thus formed had a specific surface areaof about 500 m²/m² as determined by BET method.

4-Methylstyrene was then subjected to the same reduction reaction asmentioned above. When the current efficiency was 10%, 4-ethyltoluene wasobtained.

FIG. 3 is a graph illustrating the cumulative amount of electrolyticallydeposited palladium black determined at various times by weight. Thecurrent efficiency was 24%.

FIG. 4 is a graph illustrating the relationship between the cumulativeamount of 4-ethyltoluene produced by a galvano electrostaticelectrolytic apparatus at a current density of 5 A/dm² with varioushydrogen-storing metals having palladium black deposited thereon fordifferent periods of time and the reduction reaction time. In the graph,□ indicates the measurements on the hydrogen-storing metal havingpalladium black deposited thereon for 60 minutes, ▴ indicates themeasurements on the hydrogen-storing metal having palladium blackdeposited thereon for 40 minutes, Δ indicates the measurements on thehydrogen-storing metal having palladium black deposited thereon for 20minutes, indicates the measurements on the hydrogen-storing metal havingpalladium black deposited thereon for 10 minutes, and 0 indicates themeasurements on the hydrogen-storing metal having palladium blackdeposited thereon for 0 minutes.

FIG. 5 is a graph illustrating the relationship between the depositiontime during which palladium black is deposited and the reactionefficiency of 4-ethyltoluene.

EXAMPLE 3

Using the same electrolytic cell 1 as used in Example 1, platinum blackwas deposited by the action of active hydrogen.

Reaction solution: H₂PtCl₆.6H₂O 0.1 mol/l

Electrolytic solution: 6M KOH

Current density: 5 A/dm² (50 MA)

Agitation: None

Electrical quantity: 6C

Reaction formula: PtCl₄ ²⁻+2H.→Pt+4Cl⁻+2H⁺

When the current efficiency was 20%, platinum black was deposited to athickness of 1 μm.

Using the palladium plate having platinum black deposited thereon,electrolysis was effected while 4-methylstyrene was subjected to areduction reaction in the same manner as in Example 1. When the currentefficiency was 30%, 4-ethyltoluene was obtained.

EXAMPLE 4

Using the same electrolytic cell 1 as used in Example 1, palladium blackwas deposited by the action of active hydrogen. Thereafter, platinumblack was produced on the deposit of palladium black.

Conditions of Deposition of Palladium Black

Reaction solution: PdCl₂ 5 g/dm³+HCl 1 mol/dm³

Current density: 1 A/dm² (10 mA)

Agitation: None

Electrical quantity: 5C

Conditions of Deposition of Platinum Black

Reaction solution: H₂PtCl₆.6H₂O 0.1 mol/l

Current density: 5 A/dm² (50 mA)

Agitation: None

Electrical quantity: 6C

Reaction formula: PtCl₄ ²⁻+2H.→Pt+4Cl⁻+2H⁺

Using the palladium plate thus obtained, 4-methylstyrene was subjectedto a reduction reaction in the same manner as mentioned above. When thecurrent efficiency was 80%, 4-ethyltoluene was obtained.

It can be presumed that since the platinum catalyst is a structuredeveloped on palladium black, the increase of surface area and thecatalytic activity are combined to exert the foregoing effect.

EXAMPLE 5

Using the same electrolytic cell 1 as used in Example 1, palladium blackwas deposited on a palladium plate by the action of active hydrogen.Thereafter, platinum black was electrolytically deposited on the depositof palladium black. During this process, an electric current was appliedto the palladium plate having palladium black deposited thereon as acathode provided opposing the interior of the electrolytic chamber 3filled with a plating solution.

Conditions of Deposition of Palladium Black (electroless plating)

Reaction solution: PdCl₂ 5 g/dm³+HCl 1 mol/dm³

Current density: 1 A/dm² (10 mA)

Agitation: None

Electrical quantity: 5C

Conditions of Deposition of Platinum Black (electrolytic plating)

Reaction solution: H₂PtCl₆.6H₂O 0.1 mol/l

Current density: 5 A/dm² (50 mA)

Agitation: None

Electrical quantity: 6C

The cathode thus prepared was then mounted in the same cell in such anarrangement that the platinum black side thereof faces the reactionchamber. Under these conditions, 4-methylstyrene was subjected toreduction reaction in the same manner as mentioned above. When thecurrent efficiency was 70%, 4-ethyltoluene was obtained.

EXAMPLE 6

Using the plated electrode prepared by plating a catalyst in Example 1,acetylene gas was subjected to a reduction reaction in the reactionchamber of the electrolytic cell 1 used in Example 1. The reactionconditions were as follows:

Reaction substrate: Acetylene

Temperature: Room temperature

Flow rate: 2.5 ml/min

Loading: 5 ml (1 atm)

Current density: 5 A/dm² (50 mA)

Electrolysis time: 5 hours

When the current efficiency was 60%, propylene was obtained. When thecurrent efficiency was 30%, propane was obtained.

COMPARATIVE EXAMPLE 2

The reduction reaction procedure of Example 6 was followed except thatpalladium black was not deposited. When the current efficiency was 40%,propylene was obtained. When the current efficiency was 5%, propane wasobtained.

EXAMPLE 7

Using the same electrolytic cell 1 as used in Example 1, gold wasdeposited by the action of active hydrogen.

Reaction solution: HAuCl₄.4H₂O 0.1 mol/l

Electrolytic solution: 6M KOH

Current density: 5 A/dm² (50 mA)

Agitation: None

Electrical quantity: 6C

Reaction formula: AuCl₄ ³⁻+3H.→Au+4Cl+3H⁺

When the current efficiency was 20%, gold was deposited to a thicknessof 1.5 μm.

Subsequently, electrolysis was effected at a current density of 0.5A/dm² while oxygen gas and pure water were supplied into the reactionchamber at a rate of 20 ml and 1 ml per minute, respectively, instead ofthe reaction solution for plating. When the current efficiency was 10%,aqueous hydrogen peroxide having a concentration of 6 ppm was obtained.

COMPARATIVE EXAMPLE 3

The reduction reaction procedure of Example 7 was followed except thatgold was not deposited. When the current efficiency was 5%, aqueoushydrogen peroxide having a concentration of 3 ppm was obtained.

EXAMPLE 8

Using the same electrolytic cell 1 as used in Example 1, electrolysiswas effected with the reaction chamber 6 being filled with the reactionsolution containing 1 cc of lanthanum-nickel alloy powder under thefollowing conditions. Palladium black was produced on the other surfaceand the powder surface of the cathode.

Reaction solution: PdCl₂ 5 g/dm³+HCl 1 mol/dm³

Current density: 1 A/dm² (10 mA)

Agitation: Circulation by pump

Electrical quantity: 50C

Reaction formula: Pd²⁺+2H.→Pd+2H⁺

When the current efficiency was 30%, a granular deposit having a size of0.1 μm was observed on the powder surface of the cathode on SEMphotograph.

As mentioned above, the present invention provides an electrolyticprocess which comprises effecting electrolysis with a hydrogen-storingmetal member as a cathode to produce hydrogen which is then adsorbed bythe hydrogen-storing metal member through which it is allowed to migrateto at least a part of the other surface thereof at which it is desorbedand utilized in a hydrogen reaction, wherein the hydrogen-storing metalmember is provided with a porous catalyst layer on the surface thereof.

The present invention also provides an electrolytic apparatus using theforegoing electrolytic process. In this arrangement, hydrogen thusadsorbed is desorbed to allow the catalyst to accelerate its reactionwith the reactant. Because of its porosity, the catalyst layer has alarge surface area at which the reactant can come in contact withhydrogen, making it possible to raise the reaction rate. Accordingly,even if electrolysis is effected at a great current density to producehydrogen at a high rate, the hydrogen reaction can be raisedcorrespondingly, making it possible to provide a high currentefficiency.

The present invention provides an electrolytic apparatus comprising ahydrogenation reaction applied electrode having a large surface area. Itwas confirmed that the use of this electrolytic apparatus makes it easyto reduce the reactant unprecedentedly. Thus, the use of thiselectrolytic apparatus makes it easy to develop a new synthesis process.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

What is claimed is:
 1. An electrolytic apparatus comprising anelectrolytic chamber and a reaction chamber separated by ahydrogen-storing metal member, means for charging an electrolyticsolution into said electrolytic chamber, and an anode provided in saidelectrolytic chamber opposing said hydrogen-storing metal member servingas a cathode, said hydrogen-storing metal member is adapted to adsorbhydrogen produced in the electrolytic chamber by electrolysis of theelectrolytic solution, the adsorbed hydrogen transferring to the side ofthe hydrogen-storing metal member facing the reaction chamber, and saidhydrogen-storing metal member comprising a porous catalyst layer whichis adapted to catalyze a hydrogenation or reduction reaction in saidreaction chamber between a reactive compound in contact with a surfaceof the catalyst layer and the adsorbed hydrogen.
 2. The electrolyticapparatus as claimed in claim 1, wherein said hydrogen-storing metalcomprises palladium or an alloy thereof, said porous catalyst layercomprises a metal black belonging to the platinum group or gold and thehydrogenation or reduction comprises hydrogenation of an unsaturatedhydrocarbon.
 3. The electrolytic apparatus as claimed in claim 1,wherein said porous catalyst layer formed on the surface of saidhydrogen-storing metal member is obtained by bringing a hydrogen-storingmetal member which has adsorbed hydrogen into contact with anelectroless plating solution containing a catalyst component so that thesurface of said hydrogen-storing metal member is electrolessly platedwith said catalyst metal by the action of hydrogen adsorbed in saidhydrogen-storing member.